The challenges remain the same in the aquaculture industry

Pictured: Ingunn Sommerset, Head of Fish Health at the Norwegian Veterinary Institute

Over 52 million farmed fish died before the time of slaughter in 2020. This is close to the record year of 2019 with 53 million, where the algae disaster in Nordland and Troms resulted in eight million additional deaths. The fact that salmon die prematurely is a sign that they are not doing well or are susceptible to disease.

The Fish Health Report provides an annual status of Norwegian fish health based on reported figures from farmers, fish health services, private laboratories and the Norwegian Veterinary Institute's own diagnostics.

"Although many in the industry are making great efforts, the situation with disease, lice and mortality is not improving at the national level. The explanation probably lies in an interaction of negative effects of handling-intensive lice treatments and infectious diseases, which have existed in the industry for a long time," says editor of the fish health report and specialist for fish health, Ingunn Sommerset, at the Norwegian Veterinary Institute.

The diseases infectious salmon anemia (ISA), pancreatic disease (PD) and cardiac cysticercosis (CMS) were all widespread in Norwegian fish farms in 2020. In addition, a new bacterial disease in salmon (pasteurellosis) has emerged that appears to have gained a foothold in Western Norway over the past three years.

Increased mortality from Nordhordaland to Stadt
Production area 4 (PO 4), which is the area from Nordhordaland to Stadt, has had the most negative development with 27 percent mortality, up from 19.4 percent the previous year. There is no simple explanation for this. PO 4 is the area where the most thermal delousing (short-term treatment in hot water) has been used, but the number of lice treatments per location does not differ significantly from the rest of Norway. In 2020, PO 4 had a total of 56 cases of PD, out of a total of 158 in all of Norway. Several of the locations with the highest mortality in PO 4 in 2020 had PD, but there are no figures on how much additional mortality PD causes.

ILA at highest level since 1993
There were 23 new detections of ISA in 2020, all in farmed salmon at sea. This is more than double the number in 2019 and the highest number since 1993. The disease has been detected in a total of seven production areas along the coast, but the focus has been in PO 10-12 (Troms and Finnmark) with a total of 15 detections. Approximately half of the ISA cases in 2020 are considered primary outbreaks. This means that they cannot be linked to previous outbreaks or another clear source of infection.

Pancreatic disease (PD)
The number of facilities with pancreatic disease (PD) remains at a high level. With a total of 158 new cases in 2020, this is a small increase from 2019. There has been an increase in the number of cases of PD caused by the SAV-3 variant in PO 2 (Ryfylke) and PO 4 (Nordhordland to Stadt), while there has been a decrease in PO 3 (Karmøy to Sotra). There have been no new PD cases in surveillance zone south (PO 1) or in surveillance zone north (PO 7-13).

Heartbreak (CMS)
In the survey among fish health personnel and inspectors in the Norwegian Food Safety Authority, heartworm disease (CMS) ranked top among all problems in the food fish phase that cause mortality in salmon in 2020. Based on combined data from private laboratories and the Veterinary Institute's own figures, there were 154 locations with a CMS diagnosis in 2020. The bulk of CMS outbreaks appear to be in southern and central Norway.

Need to rethink
– When the regime we have does not produce the desired results in terms of improving disease and welfare, we must think again and do something different. We can do more to reduce contact between geographical areas, try to eradicate or reduce the disease burden and consider strategic measures to reduce the need for lice treatments. Ongoing work to get a better national overview of what actually kills fish is an important measure. Research, management and the industry itself are now engaged in this, and here we will be able to gain knowledge that can provide a basis for targeted measures, explains Brun.

More results from the Fish Health Report:

• Furunculosis was detected in five sea locations with salmon in 2020, all associated with the Namsenfjord area (PO 7). Three cases of furunculosis were also detected in sea snails, two of which were in the same facility as salmon with furunculosis.
• Cardiomyopathy (CM) is a serious unlisted disease, but ranks somewhat lower as a cause of mortality. CM disease was confirmed in 161 locations
• Complex gill disease is, as the name suggests, often multifactorial and multiple infectious agents such as viruses, bacteria and parasites can be detected simultaneously. Gill disease causes mortality, reduced welfare and lower growth, and is one of the health problems that has increased the most in 2020.
• Of the diseases associated with bacteria, wound problems and infection with Moritella viscosa (classical winter wounds) and Tenacibaculum spp. (atypical winter wounds) have been important causes of reduced welfare and mortality in salmon in the sea phase. However, it is challenging to estimate the exact incidence of both classic and atypical winter wounds, since the diseases are not listed and relatively easy to diagnose in the field.
• The last three years have shown an increase in the number of detections of pasteurellosis in salmon. Aggregate figures from the Norwegian Veterinary Institute and private laboratories show that 57 different locations were detected with pasteurellosis in 2020, which is a sharp increase from 2019. The majority of the detections are in Western Norway.

Fish welfare and measures against sea lice
In 2020, the lice situation nationwide was the same as the previous year. The production of lice larvae was somewhat lower in the most exposed production areas during the migration period for wild salmon.

There was an overall increase of 21 percent in the number of weeks of drug-free lice treatments in 2020 compared to 2019, and a total of 2,983 treatments were registered in 2020.

The increase applied to thermal, mechanical and freshwater delousing, with the increase being greatest for freshwater delousing (53 percent increase from 2019 to 2020). However, thermal delousing was still the most common drug-free delousing method in 2020. Fish health personnel reported through the survey that thermal and mechanical treatments in particular resulted in increased mortality in the period after treatment.

Cleaner fish: Figures from the Directorate of Fisheries and EWA Consulting indicate a decrease in the number of exposed cleaner fish in 2020. The survey highlights, among other things, emaciation, wounds and drug-free delousing as major welfare problems for roe crackers.

The wild salmon
In 2020, the Norwegian Veterinary Institute and the Norwegian Food Safety Authority launched a national reporting system for registering sick and dead wild fish. The reporting system is part of the health monitoring of wild salmonids, and the main purpose is to detect serious incidents that have an impact on fish health in Norway. In the summer of 2020, illness and mortality were again registered in wild salmon in the Enningdal River in Østfold. The condition, which has been given the English name "red skin disease", appears shortly after sea-migrating salmon have entered the river. Similar observations have been made in several countries in Northern Europe, but a clear cause has not yet been identified. Based on the work of the Norwegian Veterinary Institute, there is little evidence that infection is a main cause.

The Ranelva (Rana River) was declared free of the parasite Gyrodactylus salaris in the fall of 2020, following an extensive control and monitoring program. The parasite poses an increasingly smaller threat to wild salmon in Norway, but we still have eight infected rivers in Norway. As the parasite occurs in our neighboring countries, close to our common border, targeted monitoring is important to prevent the importation of infection.

Link to the report: https://www.vetinst.no/rapporter-og-publikasjoner/rapporter/2021/fiskehelseraporten-2020

Contact persons:
Head of Fish Health, Ingunn Sommerset, tel. 92616360
Department Director, Fish Health and Welfare, Edgar Brun, Tel. 91123595
Communications Advisor, Tom Haavardstun, tel. 40008146